Morphological Change and Destabilization of β-Actin mRNA by Tumor Necrosis Factor in Human Microvascular Endothelial Cells

Abstract

Tumor necrosis factor-α (TNF-α) produced morphological changes from a cobblestone-like shape into a spindle shape in human omental microvascular endothelial (HOME) cells and also a drastic rearrangement of actin filaments. Expression of β-actin gene was diminished in HOME cells treated with TNF-α for 24 h. Northern blot analysis of the β-actin gene demonstrated that the cellular level of β-actin mRNA was decreased at 6-12 h after exposure to TNF-α. However, there appeared to be no changes in cellular mRNA levels of β-tubulin, fibronectin, laminin B1, laminin B2, and laminin binding protein genes after treatment with TNF-α. Nuclear run-on assays showed increased transcription of the low-density lipoprotein receptor gene, but not of the β-actin gene. These data suggested that the TNF-α-induced inhibition of β-actin gene expression was not due to altered transcription activity. The degradation rates of β-actin, plasminogen activator inhibitor-1, and epidermal growth factor receptor mRNAs were examined in the presence of actinomycin D. β-Actin mRNA was found to be specifically destabilized in TNF-αtreated HOME cells, while other mRNA species were not. Coadministration of cycloheximide blocked the TNF-α-induced degradation of β-actin mRNA. The TNF-α-induced destabilization of β-actin mRNA and rearrangement of actin filaments are discussed in relation to the morphological changes in human microvascular endothelial cells.